I did a week-long silent meditation retreat in Thailand a few years ago. I thought it would be difficult for the same reasons you mention -- I tend towards night-owling and loathe the thought of not eating for more than a few hours. It turned out to be much much easier than I expected. Without electronics and other sources of artificial light the circadian rhythm shifts to the sunrise-sunset cycle pretty rapidly. I slept quite well for the majority of my stay. As to the food, I think we're just conditioned to think we need way more than we really do. Eating two meals was only hard the first full day, and after that it felt fine. The meals were on the large side so it wasn't a large calorie deficit, if any. I definitely encourage you to try it if it's something you're interested in, you may be surprised at what you're capable of.

e: in light of what jason_slack said - your experience may vary, of course. Just saying that personally I did not find the sleeping/eating situation to be too difficult after a couple of days. My biggest struggle was actually sitting on the ground for so many hours per day. My hips and legs have become so tight from chronically sitting in an office chair that maintaining good posture on the floor was very painful for me (I've actually since started stretching regularly to work on this).